They decided to split up the investigation between the two of them.
Mikoshiba went to meet Ms. Mano in person. He read the user complaints one by one and gathered what the moms had felt was "weird"—the temperature on the ground that didn't turn into numbers.
Mio, meanwhile, stayed at the office and dove into the logs.
When recommendations go haywire, it's usually the build that's broken. So Mio started by suspecting their own code. Collaborative filtering recommends what similar users liked—she traced that heart of it line by line. The formula for choosing similar users, the order in which votes were stacked, all straight out of the textbook, nothing distorted anywhere. Even on a small test board she built, it recommended things back correctly, exactly as the votes she fed in. No bugs.
—The build is innocent.
Then what was at fault wasn't the build, but what was being fed to it.
In the evening, Mikoshiba came back.
"How is it? See anything?"
"Halfway. What about you?"
"Ms. Mano is a good person," Mikoshiba said, pulling out a folding chair. "Even after making it a company, she's kept writing articles herself for ten years. 'I just want people to be able to open it at night without worrying,' she said. I understood why Aya's so taken with her."
Mikoshiba pulled up the notes he'd taken on site.
"So, I talked directly to the people who complained. 'It used to feel like it understood how tight my wallet was, but now it's like it's talking to rich moms.' Not the kind of phrasing that shows up in numbers, but interesting, isn't it?"
"How tight her wallet was," Mio said, without taking her eyes off the screen. "But wallets aren't a parameter of collaborative filtering."
"True." For some reason, Mikoshiba laughed a little at her curtness. "But there was one thing that oddly stuck with me. One mom said this: 'It used to recommend articles on "lazy-mom baby food" that were perfect for a sloppy mother like me. Lately it's nothing but inoffensive, generic articles.'"
"...The outline of 'similar' has blurred." Mio's fingers stopped, slightly. "A large amount of something faintly similar to everyone got mixed in, and the sharp edge that had hit only her got smoothed down and disappeared."
"Does that have anything to do with it?"
"I don't know," Mio answered honestly. That one remark alone, she stored somewhere different from the other numbers. She couldn't grasp yet where to connect it.
The next day, Mio set about suspecting the votes themselves.
She peered into the gray product articles and the accounts that had given high stars, one by one. But the likes and ratings didn't differ a hair from those of genuine hit articles, and every account had attached an inoffensive little review. Looked at individually, there wasn't a fingerprint of malice left anywhere.
In that case, Mio thought, and started working on how the votes were handled. Trust them all and rebuild, and that unknown baby carrier shot up to the top. Conversely, use anomaly detection to reject ratings that were too high—and longtime regulars who had been coming for ten years and dutifully leaving "likes" were deemed "abnormally active" precisely because of their enthusiasm, and got caught wholesale in the net. A net that cut off first the very customers you should value most.
"...Whichever way I lean, it slips," Mio said, covering her face with both hands. "Trust it, and it recommends dirty things. Doubt it, and it cuts real customers."
Just then, Mikoshiba leaned in to look at her profile.
"So. How are things?"
Mio hesitated a little. She pressed a temple once.
"...I'm looking into the possibility that the voting's been hijacked by shills," Mio said slowly. "An unknown theater troupe seats a hundred hired people in the audience. They applaud at every line, and when it's over they give a standing ovation. The survey comes back as unanimous rave reviews. But the real audience is left behind, staring blankly."
"The number of claps is real. But the ones clapping are hired audience members."
"Right. I'd been counting the 'number' of claps the whole time. The more I counted, the more the shills dragged me along." Mio glared at the too-clean waveform. "So I stopped counting and suspected the shills. But even when I go look at the audience members individually, they don't seem to be shills."
Mio sank back into her chair.
When night came, Aya Shinkai had stopped her design work and was looking over.
"Mio. It's turned into a bird's nest again." Aya pressed her forehead in exasperation. "How many hours have you been sitting there with that frown?"
"Don't touch it. I'm thinking."
Mikoshiba quietly set two cans of coffee on the edge of Mio's desk. One black, the other a sweet one with lots of sugar. Mio's fingers didn't stop.
One of Mikoshiba's hands was still gripping the stopwatch. On the secondary display, a recording of the afternoon's bouts played soundlessly. His thumb came down at the initial charge, stopped at the decision, and on to the next bout.
"...You're still timing those?" Mio's voice was half exasperated.
Mikoshiba's hand didn't stop. "...I meant to take it over for you, but sumo itself turned out to be more interesting than I expected."
Mio glanced at the thumb meticulously beating out the same rhythm and turned back to the screen.
Just then, Aya stopped working on her color proof. In a no-big-deal tone, she let it spill out as if talking to herself.
"You know, I can't tell fake likes or shill reviews apart just by looking at them at all. Each one looks exactly like the real thing." Aya put down her mouse. "But I can kind of tell. By the 'way they press it.' Real people press it more randomly, on a whim, right? Just, plink, whenever they feel like it."
The way they press it.
Mio's fingers stopped in midair.
That was it. Glaring at the accounts one at a time turned up nothing. Whether it was real or fake wasn't written inside that one vote. Where it surfaced was—only in the way the bundled distribution fluctuated.
One article at a time. One account at a time. She had peered at them one by one, and each was innocent, and nothing came out. The unit she'd been looking at was wrong. Not a single vote, but the way they pressed it. Not points, but fluctuation.
"...Mio, that face." Aya sensed something and half raised her head. "Are you starting to see something again?"
The sounds of the world receded abruptly. The desk, the canned coffee, the voices of the two beside her, none of it was in her field of view anymore.
"...It connects."
Mio murmured it, almost on a breath. Then she let go of the coffee, swiveled her chair, and turned back to the screen.
"Ah, here it goes." Aya drew back half a step, smiled wryly, and shrugged. "...No matter how many times I see it, I can't get used to it. Hey, Boss, what kind of face am I supposed to make at times like this?"
There was no reply from Mikoshiba.
Mikoshiba, too, had at some point sunk into his own swamp. The deeper Mio dove, the more his hands ticked the stopwatch in the same rhythm. And yet, without taking his eyes off the screen, his free hand alone reset the sweet canned coffee on the edge of Mio's desk. Only the caretaking had been unconsciously automated.
"...And they're both gone," Aya said, lifting her own can for lack of anything else to do.
To an onlooker, it was just one woman furiously pounding at a keyboard. But inside Mio, the unnatural lack of wobble from a few dozen people, sunk at the bottom of a vast sea of votes, suddenly formed an image visible only to her eyes. Seeing far, wide, in a single breath. It was a moment that could be called nothing but clairvoyance.
That night, the world vanished from the Gotanda office.
She stopped counting the "number" of votes and rebuilt it to measure the "way they fluctuated"—how scattered they were when bundled together. Only fragments of words dropped from her mouth.
"...Not the number. The shape... bundled together, they're too uniform. ...Humans aren't this well-behaved."
Guess, then verify. Guess, then erase.
"...If it's only 'too orderly,' it'll cut the real ones too..."
Mio's fingers stopped there, once.
"...No. Not pull them out. Mark them—and in the end, hand them to a person."
The sweet canned coffee had gone cold at some point, without her having touched it once.
Outside the window, indigo was changing to a whitish gray. One by one, green lamps lit on the last verification items.
"...All green."
Mio sank limply against the back of her chair. She was dried out to the core. Even so, her eyes alone still shone.
The weapon was ready. All that was left was to unveil it on site.
Mio got up sluggishly and grabbed her jacket.
"...Let's go, Mikoshiba."
No sooner had she said it than Mio reached for the secondary display, where a bout was still playing without a decision, and abruptly shut off the recording. Mikoshiba's fingers, which had gripped the stopwatch all night, were left with nowhere to go over the halted bout. She apparently had no intention of waiting for an answer from the start.
Mikoshiba looked once at the darkened screen. Then he took the car keys and followed the small back that had already gone out the door ahead of him.